In semiconductor manufacturing, ion implantation is a common technique for altering properties of semiconductor wafers during the production of various semiconductor-based products. Ion implantation may be used to introduce conductivity-altering impurities (e.g., dopant implants), to modify crystal surfaces (e.g., pre-amorphization), to created buried layers (e.g., halo implants), to create gettering sites for contaminants, and to create diffusion barriers (e.g., fluorine and carbon co-implant). Also, ion implantation may be used in non-transistor applications such as for alloying metal contact areas, in flat panel display manufacturing, and in other surface treatment. All of these ion implantation applications may be classified, generally, as forming a region of material property modification.
In many doping processes, a desired impurity material is ionized, the resulting ions are accelerated to form an ion beam of a prescribed energy, and the ion beam is directed at a surface of a target substrate, such as a semiconductor-based wafer. Energetic ions in the ion beam penetrate into bulk semiconductor material of the wafer and are embedded into a crystalline lattice of the semiconductor material to form a region of desired conductivity.
An ion implanter usually includes an ion source for generating ions. Ion sources generate a large amount of heat during operation. The heat is a product of the ionization of a working gas, resulting in a high-temperature plasma in the ion source. To ionize the working gas, a magnetic circuit is configured to produce a magnetic field in an ionization region of the ion source. The magnetic field interacts with a strong electric field in the ionization region, where the working gas is present. The electrical field is established between a cathode, where the cathode emits electrons, and a positively charged anode. The magnet circuit is established using a magnet and a pole piece made of magnetically permeable material. The sides and base of the ion source are other components of the magnetic circuit. In operation, the ions of the plasma are created in the ionization region and are then accelerated away from the ionization region by the induced electric field.
Notably, the magnet is a thermally sensitive component, particularly in the operating temperature ranges of many ion sources. For example, in many end-Hall ion sources cooled solely by thermal radiation, discharge power may be limited to approximately 1000 Watts, and ion current may be limited to approximately 1.0 Amps to prevent thermal damage particularly to the magnet. To manage higher discharge powers, and therefore higher ion currents, direct anode cooling systems have been developed to reduce the amount of heat reaching the magnet and other components of an ion source.
One such anode cooling system includes coolant lines running to and pumping coolant through a hollow anode. Specifically, material from the ion source is removed (e.g., using a subtractive manufacturing process) to form two axial conduits along a length of the sidewall of the ion source, wherein the axial conduits may be spaced 180 degrees apart. Unfortunately, this axial conduit configuration limits the ability to provide uniform cooling throughout the ion source.